Directed self-assembly (DSA) is an emergent nano-lithography approach in which self-assembling block copolymer thin films (BCP) are ordered using larger-scale, pre-defined guides patterned by standard lithography. Typically, lamellar (line/space) or cylindrical (arrays of dots) copolymer pattern morphologies are spatially templated by either topographic relief or patterned chemical inhomogeneity on the substrate. Commensurability between the guiding feature spacing and the natural pitch of the copolymer induces a high degree of position and orientation order in the self-assembled, nanoscale patterns. However, directed self-assembly is limited in the range of structures that can be fabricated in a single layer because each BCP material defines only a single equilibrium morphology.
These approaches still rely on a single morphology to generate patterns, controlling the type of pattern formed by the orientation of the morphology relative to the surface. For example, a cylinder oriented surface-perpendicular produces a circular hole, while the same cylinder oriented surface parallel produces a line. Defining the pattern by orientation control is not ideal for fabrication, most notably during subsequent pattern transfer processes, as the perpendicular and parallel orientations require different considerations during these steps.